Complex alkali metal soap-alkaline earth metal salt thickened grease composition



United States Patent COMPLEX ALKALI METAL SOAP-ALKALINE EARTH METAL SALT THICKENED GREASE COMPOSITION Arnold J. Morway, Clark Township, Union County, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application January 2, 1952, Serial No. 264,683

14 Claims. (Cl. 252-40) The present invention relates to an improved lubricating grease composition and method of manufacturing such a composition. In particular, the invention relates to a lubricating grease having unusual properties such as a combination of high dropping point, good mechanical stability under widely varying temperatures, substantial insolubility in water and good yield or consistency with a low soap content. The product is relatively inexpensive, considering its unusual properties. It possesses several advantages which are not common in prior art solid or semisolid lubricating materials.

It has previously been suggested in the art that lubricating greases may be prepared by thickening appropriate lubricating oils with complex salt-soap thickeners in lieu of the conventional simple soaps of higher fatty acids. Thus, in United States Patent No. 2,487,080 and in some contemporary publications it has been suggested that short fibre, high temperature soda base grease may be prepared by adding to a lubricating oil proportions of 30 to 60% by weight of conventional high molecular weight fatty acid soap in combination with an alkali metal salt, e. g. sodium salt, of a short chain aliphatic acid such as formic, acetic, hydroxy acetic, lactic, propionic, butyric and related carboxylic acids of low molecular Weight. The latter acids, it is suggested, may be used in proportion of 0.1 to of the said entire grease composition. In this product it will be noted that the total proportions of thickener to oil are quite high, considering both the salt and the soap to be thickeners In other patents, e. g. U. S. patents to McLennan, Nos. 2,417,428 to 2,417,433 inclusive, a number of grease compositions are disclosed Wherein a low molecular weight acid, specifically acetic acid is added during, or after, saponification of the higher fatty acid which is commonly used for the making of lubricating greases. This acetic acid presumably is'converted to the salt of the same metal which saponifies the soap, an excess of the latter, or the base containing it, being employed to make salt and soap simultaneously or seriatim. Thus, in U. S. Patent No. 2,417,428 for example, greases of calcium, sodium, strontium, lithium and other metals are described. In each of these the acetic acid utilizes some of the metal base. The resulting product, therefore, contains the high molecular weight soap of the metal base and the acetate of the same base.

In other examples, such as U.-S. Patent No. 2,516,136 issued to the present inventor and a co-inventor, it has been suggested that certain high molecular weight fatty acid soaps may be modified by forming therewith or therein a salt of a low molecular weight cyclic carboxylic acid such as furoic acid. Here again the same metal base is used to saponify or neutralize both the high molecular weight fatty acid and the low molecular weight carboxylic acid in forming the complex thickeners. Because of possibilities of double decomposition and degradation of products, the prior art has generally avoided the use of salts of one metal base with soaps of a different metal base.

The present invention differs from all the foregoing, and

2,719,122 Patented Sept. 27, 1955 others which are similar or related, in utilizing a combination of a monovalent metal and preferably an alkali metal soap of the high molecular weight fatty acids, saturated or unsaturated. Preferably a lithium soap is used, in combination with a dry powdered divalent metal salt, preferably an alkaline earth metal salt of a low molecular weight carboxylic acid. The C1 to C5 saturated or unsaturated fatty acids such as acetic, propionic, acrylic or methacrylic, or other low molecular weight acids which form a similar complex, such as furoic acid, its thio equivalent, and like acids may be used for the salt constituent. 1

The proportions of the soap and the salt must be rather closely controlled for best results so that they are approximately equimolar. Water solutions of soap or salt or even the presence of water must be avoided to prevent double decomposition.

Specifically, a preferred thickening agent consists of substantially equimolar proportions of lithium soap of fatty acids of the C12 to C22 range and alkaline earth metal salts, e. g. calcium acetate, etc. The lithium soaps are preferably of the saturated fatty acids and are more particularly those which average about 18 carbon atoms per molecule in chain length. The lithium soap is complexed or combined with the alkaline earth metal salt of the lower saturated fatty acids. The calcium salts of the fatty acids and especially calcium acetate are particularly preferred but the other alkaline earth metal salts may be used and may be derived from the other acids mentioned above.

The method of manufacturing the grease of the present invention differs particularly from the prior art in several respects. The monovalent metal soap of the higher fatty acids is either preformed and added to the oil as a dry powder or it is formed in situ (in mineral oil) and completely dehydrated before the low molecular Weight salt is added. The latter also is added as a dry powder. A concentrate preferably is formed first, being cut back later by working in additional oil. After the first concentrate has been prepared, enough oil should be added to permit complete dispersion of the solids (soap and salt) when heated. It may be desirable to add still further oil later to obtain a softer grease.

The temperature of the mass, after addition of oil, is raised to such a point that the grease is completely melted or the crystal structure of the soap or complex is fully disrupted. As the mixture is cooled, a stable grease structure is established, apparently by crystallization of the complex thickener in the oil. This thickener, formed according to the process of the present invention, imparts to the grease properties which have not been attained and which would not be expected from a knowledge of properties of the separate constituents. By the anhydrous method of soap-salt dispersion the base exchange of soaps is prevented. The formation of high molecular Weight soaps of the divalent metal and of low molecular weight salts of the monovalent metal is effectively inhibited. Hence objectionable side reactions do not occur. The combination product has substantially greater thickening power and superior water resistance. It shows superior oxidation inhibition with moderate amounts of conventional inhibitors. The resulting grease shows excellent mechanical stability over a wide range of operating temperatures.

In general, the greases of the present invention have lower proportions of thickener for a given consistency than many prior art compositions. The proportions of thickener may vary rather widely, depending upon the specific purpose of the grease. For soft greases they may range from about 4% to 8 or 10% by weight of combined salt and soap. For harder greases, proportions may be as high as 30% but a preferred range, for most purposes, is between about 8 and 15%.

The composition of the present invention has other outstanding properties. It has excellent structural stability at relatively very high and very low operating temperatures. Since greases of firmconsistency can be made-with relatively very low soap or soap-salt contents, the products can be made inexpensively. I The methodfor their formulation, furthermore, is quite simple and straightforward.

The invention will be more fully understood by reference to the following specific examples:

Example I A stiff grease or soap concentrate was prepared using 20% by weight of fatty acid. In lieu of stearic acid, which is often preferred for greases of high quality, the substantially saturated hydrogenated fish oil acids of average chain length of about C18, sold commercially under the trade names Hydrofol Acids 51 or Hydrofol Acids 54, may be used. These are quite fully equivalent to. stearic acid. In this example Hydrofol Acids 54 were neutralized with 3.3% by weight of lithium hydroxide monohydrate. The soap was prepared in situ and the grease dehydrated. Then 5% of dry calcium acetate which had been previously prepared was added, plus 1% by weight of a phenyl naphthylamine, specifically phenyl-alpha-naphthylamine. Other oxidation inhibitors may be used quite satisfactorily. In some cases they may be omitted, e. g., where the grease is frequently or continuously replaced in service. The remainder of the composition consisted of 70.7% of a mineral base lubricating oil having a viscosity of about 55 S. S. U. at 210 F. The grade or viscosity of the oil may be varied, of course, depending upon the type of lubrication needed.

The following procedure was followed in detail. The Hydrofol Acid 54, and about one-third of the mineral oil were charged to a fire heated kettle and warmed to 150 F., to melt the acid and dissolve it in the mineral oil. Thereafter, the lithium hydroxide was added in an aqueous solution to neutralize the fatty acids. Soap was formed and the resulting concentrate in oil was dehydrated by heating it to a temperature of 275 to 300 F. Thereafter the previously prepared calcium acetate in the form of a dry powder was added. The mass was heated further to a temperature of 470 F. During this heating period the additional mineral oil was added gradually, while stirring was continued. Thereafter the grease was allowed to cool to below 250 F. with continued stirring.

The grease, formed as described above, contained about 27% of thickener. It was a hard, smooth, uniform cake having a worked penetration (60 strokes with the standard ASTM hole worker plate) of 85 mm./ 10. The product of Example I had a free alkalinity of 0.29%, calculated as sodium hydroxide, and a dropping point of over 420 F. It will be noted that this grease had a very hard consistency in proportion to its soap content, as compared with conventional greases. It was thereafter diluted, or cutback, by stirring additional mineral oil into the grease until the over-all soap-salt or complex thickener content was about 6% by weight. The'cut-back or diluted grease product was then passed through a homogenizing apparatus under high shear conditions and tested for characteristic properties. It had an unworked penetration of 320 mm./ 10. Its worked penetration, with a standard ASTM grease worker operated for 60 strokes with a 44" hole plate, was 348 mm./1(). Its dropping point was 321 F.

The product also was tested for oxidation stability. In the Norma-Hoffman bomb oxidation test, where a sample of grease is placed under 110 p. s. i. initial pressure of oxygen at 210 F., the product of Example I showed more than 524 hours to a 5 p. s. i. drop in pressure. This is considered excellent performance. Oil separation in the 60 mesh cone test was only 2.0% after 50 hours storage at 210 F., which is quite outstanding. Structural stability was shown by working the Cal 4 product 100,000 strokes at 77 F. in the standard churn type ASTM grease worker, equipped with the fine hole worker plate (325 holes of inch diameter). The product, which had an unworked penetration of 320 mm./10, increased in penetration only to 355 mm./ 10 in this severe test. It was insoluble in boiling water.

Example 11 A second product was made according to the following formula in percentage by weight:

Per cent Hydrofol acids 51 15.0 Lithium hydroxide monohydrate 2.48 Dry preformed calcium acrylate 4.0 Phenyl alpha naphthylamine 1.0

Mineral oil of 55 S. S. U. viscosity at 210 F 77.5

This product was prepared in the same manner as the grease of Example I. The finished grease had the following properties:

Free alkalinity. 0.18% as NaOH.

Appearance-Smooth, uniform, homogeneous.

Penetrations at 77 F. in mm./ 10:

Unworked Worked 60 strokes with A hole plate Worked 100,000 strokes with fine hole plate 245 Dropping point-430 F.

SolubilityInsoluble in boiling water.

Oxidation stability0ver 500 hours to a 5 lb. drop in oxygen pressure in the Norma-Hoffman bomb test.

A grease was made using a synthetic ester oil instead of mineral oil, according to the following example. In this case it was important to use a preformed drp soap as well as a dry salt because formation of soap in the ester would cause hydrolysis and some degradation of the basic lubricant oil.

Example III Ingredients were combined in proportions by weight as indicated.

Per cent Dry lithium stearate (fine powder) 21.0 Calcium acetate powder 5.0 Phenyl alpha naphthylamine 1.0 Di-Z-ethyl hexyl sebacate. 73.0

The dry lithium stearate and the sebacate ester were charged to a fire heated grease kettle equipped with stirring means for efiicient agitation.- The mixture was warmed to 300 F. while stirring. At this temperature the soap began to gel the fluid, though it had not been completely dispersed. The dry powdered calcium acetate was then added and the mass heated to 525 F. At this temperature all the soap and all but a trace of the calcium acetate had gone into solution in the ester. The product was cooled to 200 F. while stirring was continued. It. was then removed from the kettle, filtered, and packaged. It had the following properties:

Appearance-Smooth, opaque, homogeneous. Penetrations77 F., mm./ 10.

Worked 60 strokes, A hole plate 230 60,000 strokes, fine hole plate 265 Dropping point370 F. Free acidity0.59% as oleic acid.

It would be advantageous to use slightly more alkali, since experience has shown better performance with greases that are slightly on the alkaline side, as a general rule.

Example IV The product of Example III was diluted by adding one weight proportion of di-2-ethyl hexyl sebacate to two proportions of grease. It was homogenized by passing it twice through a Morehouse Mill having a clearance of 0.006.

The product had the following properties:

Dropping point-338 F. Penetration at 77 F., mm./l0.

Unworked 312 Worked 60 strokes with A" hole plate 320 Insoluble in boiling water.

It will be understood that variations may be made in overall thickener content as well as in grade, viscosity, or type of oil. Conventional additives such as extreme pressure agents, oiliness agents, thickeners, metal deactivators, oxidation inhibitors, plasticizers, and the like, may be incorporated in usual proportions as will be obvious to those skilled in the art.

What is claimed is:

1. A lubricating grease composition comprising a major proportion of grease-forminglubricating oil and a minor grease-thickening proportion of a complex thickener, said thickener consisting essentially of alkali metal soaps of saturated fatty acids of the C12 to C22 range and alkaline earth metal salt of monobasic carboxylic acids of the C1 to C5 range in substantially equimolar proportions. 5

2. A lubricating grease composition comprising a major proportion of grease-forming lubricating oil and a minor grease-thickening proportion of a complex thickener, said thickener consisting essentially of about equimolar proportions of alkali metal soap of saturated fatty acids of the C1: to C22 range and alkaline earth metal salt of saturated fatty acids of the C1 to C4 range.

3. Composition according to claim 2 wherein said oil is a mineral base oil.

4. Composition according to claim 2 wherein said lubricating oil is aliphatic dicarboxylic acid ester base oil.

5. Composition according to claim 2 wherein said soap is a lithium soap.

6. Composition according to claim 2 wherein said salt is a calcium salt.

7. Composition according to claim 2 wherein said calcium salt is calcium acetate.

8. A lubricating grease composition comprising a major proportion of a mineral base lubricating oil and 4 to 30% by weight, based on the total composition, of a complex thickener consisting essentially of equimolar parts of the lithium soap of substantially saturated fatty acids of about C18 average chain length and calcium acetate.

9. Composition according to claim 8 to which is added about 0.5 to 2% of a phenyl amine oxidation inhibitor.

10. Composition according to claim 8 in which the total thickener content is about 5 to 15%.

11. The process of preparing a lubricating grease which comprises incorporating alkali metal soap of substantially saturated higher fatty acids into a relatively small amount of grease-forming lubricating oil, heating to dehydrate, thereafter adding a dry calcium salt of C1 to C5 monobasic carboxylic acid in about the same molar proportions as the soap, heating under anhydrous conditions to a temperature sufiiciently high to substantially completely melt the salt and soap, cooling to form a stiff grease, and thereafter blending in additional lubricating oil to form a smooth softer grease.

12. Process according to claim 11 wherein the soap is lithium soap and the salt is calcium acetate.

13. Process according to claim 11 wherein the soap is formed in situ in mineral base lubricating oil.

14. A lubricating grease composition comprising a major proportion of a grease-forming lubricating oil and a minor grease-thickening proportion of a complex thick ener consisting essentially of an alkali metal soap of saturated fatty acid of the C12-C2z range and an alkaline earth metal salt of monobasic carboxylic acid of the C1-C5 range in substantially equimolar proportions, said thickener being formed by melting and cooling a mixture of said soap and salt in at least a portion of said oil under anhydrous conditions.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,082 Zimmer et al. Jan. 25, 1949 2,182,137 Ricketts Dec. 5, 1939 2,417,428 McLennan Mar. 18, 1947 2,495,651 Butcosk Jan. 24, 1950 

1. A LUBRICATING GREASE COMPOSITION COMPRISING A MAJOR PROPORTION OF GREASE-FORMING LUBRICATING OIL AND A MINOR GREASE-THICKENING PROPORTION OF A COMPLEX THICKENER, SAID THICKENER CONSISTING ESSENTIALLY OF ALKALI METAL SOAPS OF SATURATED FATTY ACIDS OF THE C12 TO C22 RANGE AND ALKALINE EARTH METAL SALT OF MONOBASIC CARBOXYLIC ACIDS OF THE C1 TO C5 RANGE IN SUBSTANTIALLY EQUIMOLAR PROPORTIONS. 